If the font is too big it may not display. Try increasing the size of the text box. Especially with a score, you may want to make it really wide too depending on how high your score goes. So the text has room as the score goes up.
Say your Score variable is "Points" and your score text is called "ScoreBoard" Whenever you have the score change have an action that says Set "ScoreBoard" to points. When you type it in it should show a dropbox of items. Select your variable for the Score, in this example, "Points".
So score changes Set "ScoreBoard" to "Points" as in the variable for the score.